JP2012224487A - Kiln tool for manufacturing positive electrode active material of lithium secondary battery, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a kiln tool having high corrosion resistance to a lithium component diffusing from a raw material while manufacturing a positive electrode active material by firing.SOLUTION: This kiln tool for manufacturing a positive electrode active material of a lithium secondary battery comprises a ceramic raw material containing β spodumene. Preferably, the content ratio of LiO in the kiln tool is 1-12 mass%, the content ratio of AlOis 15-40 mass%, and the content ratio of SiOis 55-75 mass%. Further preferably, the content ratio of NaO in the kiln tool is ≤1 mass%, the content ratio of KO is ≤2 mass%, and the sum total of both components is ≤3 mass%.

Description

  The present invention relates to a kiln tool used for manufacturing a positive electrode active material of a lithium secondary battery and a method for manufacturing the same.

  Lithium transition metal composite oxides such as lithium cobaltate, lithium manganate, and lithium nickelate are useful materials as positive electrode active materials for lithium secondary batteries. These lithium transition metal composite oxides are generally fired in a firing furnace by placing a mixture of lithium carbonate and a transition metal compound such as transition metal oxide or transition metal hydroxide in a ceramic tool such as a ceramic mortar. It is manufactured by doing. Spinel, cordierite, mullite, and the like are known as ceramic materials used for such mortars.

When a lithium transition metal composite oxide is produced by firing a mixture of lithium carbonate and a transition metal compound, during firing, Li ₂ O, which is a strongly alkaline substance, reacts with the ceramic material of the kiln tool, and the ceramic material Is known to deteriorate. Therefore, when a conventional kiln tool is used, the number of times of repeated use is limited due to a decrease in thermal shock property accompanying deterioration of the material. Therefore, various kiln tools having high alkali resistance have been proposed.

  For example, Patent Document 1 describes a mortar containing 30% to 70% by weight of spinel, 15% to 70% by weight of cordierite, and 0% to 35% by weight of mullite. In Patent Document 2, a plastic clay from which quartz has been removed or finely pulverized, an alumina component, and a clay component are mixed and molded, and fired at 1100 ° C. to 1350 ° C. to produce a porous ceramic reaction vessel. It is described.

JP 2009-292704 A JP 2010-013316 A

  However, the materials used for kiln tools such as mortars that have been proposed so far cannot be said to have sufficient alkali resistance, and the number of repeated use of kiln tools has not been greatly increased. Therefore, the subject of this invention is providing the kiln tool for positive electrode active material manufacture of the lithium secondary battery which can eliminate the various fault which the prior art mentioned above has, and its manufacturing method.

  As a result of diligent investigations by the present inventors to solve the above-mentioned problems, the use of a ceramic material originally containing a lithium component as a material for a kiln tool is higher than the lithium component contained in the raw material of the positive electrode active material. It was found that corrosion resistance can be obtained.

  The present invention has been made on the basis of the above knowledge, and has solved the above problems by providing a kiln tool for producing a positive electrode active material of a lithium secondary battery made of a ceramic material containing β-spodumene. .

In addition, the present invention provides a suitable method for producing the kiln tool,
The present invention provides a method for producing a kiln tool comprising the steps of forming a mixed powder containing petalite and kaolin into a desired kiln tool shape and firing the molded body in an oxygen-containing atmosphere.

  The kiln tool of the present invention has high corrosion resistance against the lithium component that diffuses from the raw material during the production of the positive electrode active material by firing, and the deterioration rate of the material is difficult to proceed. Moreover, since the thermal shock resistance of the material itself is excellent, the number of repeated use is improved.

1 is a powder X-ray diffraction pattern of the kiln tool obtained in Example 1. FIG. FIG. 2 is a microscopic image obtained by cutting out a vertical section of the bottom surface portion of the kiln tool of Example 1 after manufacturing lithium manganate and observing the section with an optical microscope. FIG. 3A is a microscopic image obtained by slicing a longitudinal section of the bottom surface portion of the kiln tool of Example 2 after producing lithium manganate and observing the section with a scanning electron microscope. FIG. FIG. 3D is an element mapping image of aluminum, silicon and manganese in FIG.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The kiln tool of the present invention is used as a container for storing raw materials when producing a positive electrode active material of a lithium secondary battery. The kiln tool is sometimes called a tray, a sheath, a mortar, a container, etc., but the substance is the same, and a rectangular or circular bottom part placed on the hearth of the firing furnace, It has a closed wall surface portion that rises from the periphery of the bottom surface portion, and includes a shape having an open top. In addition, kiln tools may be used like a container by combining a frame and a plate.

The positive electrode active material of a lithium secondary battery produced using the kiln tool of the present invention is generally composed of a lithium transition metal composite oxide, a lithium transition metal composite phosphate, or the like. Examples of such an oxide include a compound represented by LiMO ₂ (M represents one or more transition metals), LiM ₂ O ₄ (M represents one or more transition metals). And a compound represented by LiMPO ₄ (M represents one or more transition metals). Specific examples include lithium cobaltate, lithium manganate, lithium nickelate, olivine-type lithium iron phosphate, and lithium manganese spinel. When the active material is a lithium transition metal composite oxide, the raw material of the positive electrode active material is a mixture of a lithium-containing compound and a transition metal compound. When the positive electrode active material is a lithium transition metal composite phosphate, the raw material is a mixture of a lithium-containing compound, a phosphoric acid compound, and a transition metal compound. Examples of the lithium-containing compound include lithium carbonate and lithium hydroxide. Examples of transition metal compounds include transition metal oxides, transition metal hydroxides, transition metal sulfates, acetates, halides, and the like. Examples of the phosphoric acid compound include phosphoric acid, monohydrogen phosphate, and dihydrogen phosphate.

As described above, since the raw material for producing the positive electrode active material of the lithium secondary battery contains a lithium-containing compound, Li ₂ O and the like are produced when the positive electrode active material is produced by firing the raw material. Lithium component is produced. This lithium component reacts with the ceramic material that constitutes the kiln tool that contains the raw material, and causes the ceramic material to deteriorate. On the other hand, in the present invention, when a material that originally contains a lithium component is used as a ceramic material constituting the kiln tool, the corrosion resistance to the lithium component generated from the material is significantly improved, and the material itself is It has been found that there is little decrease in thermal shock resistance, and the present invention has been completed. Specifically, by using β-spodumene, which is a lithium aluminosilicate, as a ceramic material originally containing a lithium component, the corrosion resistance to the lithium component generated from the raw material is remarkably improved, and a material that is originally excellent in thermal shock resistance As a result, it has been found that even when used repeatedly, the thermal shock resistance is hardly lowered.

Spodumene is a ceramic material represented by LiAlSi ₂ O ₆ . It is known that spodumene has α type which is a low temperature stable phase and β type which is a high temperature stable phase. In the present invention, β-spodumene, which is a spodumene having higher corrosion resistance to the lithium component, is used. The kiln tool of the present invention may be composed only of β-spodumene, or may be composed of another ceramic material in addition to β-spodumene. Examples of other ceramic materials include alumina, silica, and mullite.

  When the kiln tool of the present invention includes β-spodumene and other ceramic materials, the proportion of β-spodumene in the kiln tool is 10 to 60% by mass, particularly 30 to 55% by mass, and the corrosion resistance to the lithium component Is higher from the viewpoint of providing a thermal shock resistance sufficient for repeated use with respect to the firing temperature of the positive electrode material. It can be identified by X-ray diffraction, for example, what kind of ceramic component the kiln tool of the present invention is composed of. Further, for example, when the kaolin is contained in β-spodumene, the ratio can be obtained semi-quantitatively by comparing the heights of the first peak of β-spodumene and the first peak of kaolin. it can.

From the viewpoint of further improving the corrosion resistance of the kiln tool of the present invention, the content ratio of Li ₂ O in the kiln tool is preferably 1 to 12% by mass, more preferably 1.5 to 10% by mass, and still more preferably 1.5 to Set to 3% by weight. The content ratio of Al ₂ O ₃ is preferably set to 15 to 45 mass%, more preferably 18 to 40 mass%. The content of SiO ₂ is preferably 50 to 75 wt%, more preferably set to 60 to 72 mass%. The content ratio of each of these oxides can be measured by, for example, fluorescent X-ray elemental analysis. Moreover, the content ratio of each oxide is controlled by adjusting the blending ratio of the raw material containing Li component such as petalite which is a raw material used when manufacturing the kiln tool and the raw material not containing Li component such as kaolin. be able to.

From the viewpoint of further improving the corrosion resistance of the kiln tool of the present invention, it is desirable to reduce the amount of alkali metal (excluding lithium) contained in the kiln tool as much as possible. Specifically, the content ratio of Na ₂ O in the kiln tool is preferably 1% by mass or less, more preferably 0.7% by mass or less. For K, which is an alkali metal like Na, the content ratio of K ₂ O in the kiln tool is preferably 2% by mass or less, more preferably 1.5% by mass or less. Furthermore, the total content of Na ₂ O and K ₂ O is preferably 3% by mass or less, more preferably 2% by mass or less, from the viewpoint of reducing the total content of alkali metals (excluding lithium) as much as possible. The content ratio of these alkali metal oxides can be measured by the same method as the content ratio of Li ₂ O or Al ₂ O ₃ described above. In order to reduce the amount of alkali metal (excluding lithium) as much as possible, a low content of Na or K may be used as petalite and kaolin, which are raw materials used when manufacturing kiln tools.

In addition to the alkali metals such as Na and K described above, in the kiln tool of the present invention, it is desirable to reduce the amount of the iron component as much as possible from the viewpoint of further improving the corrosion resistance. Specifically, the content ratio of Fe ₂ O _{3 in} the kiln tool is preferably a small amount of 0.5% by mass or less, more preferably 0.3% by mass or less. Content of the iron component can be measured by the same method as the content of Li ₂ O, Al ₂ O _3, or the above. In order to reduce the amount of the iron component as much as possible, a material having a low content of Fe, which is an impurity, may be used as petalite and kaolin, which are raw materials used when manufacturing a kiln tool.

  The kiln tool of the present invention preferably has a bulk specific gravity of 1.5 to 2.5, and more preferably 1.65 to 2.3. Further, the porosity is preferably set to 5 to 40%, more preferably 10 to 37%. The thermal shock resistance of the kiln tool can be increased by setting the bulk specific gravity to be equal to or higher than the lower limit value or to setting the porosity to be equal to or lower than the upper limit value. Moreover, the intensity | strength of a kiln tool can be raised and generation | occurrence | production of a crack etc. can be effectively prevented by making a bulk specific gravity below the said upper limit or making a porosity more than the said lower limit. The bulk specific gravity is calculated, for example, by measuring the mass of the kiln tool and dividing this by the volume obtained from the measurement of the size of the kiln tool. The porosity can be calculated from a formula of (1-bulk specific gravity / apparent specific gravity) × 100. Here, the apparent specific gravity is a value obtained by dividing the mass of the kiln tool by the mass of 4 ° C. water having the same volume as the apparent volume (JIS R2001), and is measured by the Archimedes method. The bulk specific gravity and the porosity can be adjusted by adopting an appropriate method as a molding method of the molded body to be baked in the production process of the kiln tool of the present invention. For example, when a molded body is molded by hydraulic molding, it is easy to manufacture a kiln tool having a high bulk specific gravity and a low porosity. When a molded body is formed by casting, it is easy to manufacture a kiln tool having a low bulk specific gravity and a high porosity.

  The kiln tool of the present invention preferably has a normal temperature bending strength measured according to JIS R2619 of 5 to 60 MPa, particularly 10 to 60 MPa. Further, it is preferably 5 to 70 MPa, particularly 8 to 60 MPa, particularly 8 to 45 MPa at 1000 ° C. The vicinity of 1000 ° C. is a typical use temperature of the kiln tool of the present invention, that is, a firing temperature of the raw material of the positive electrode active material. When the kiln tool has bending strength in this range, the number of repeated use can be further increased in combination with the high corrosion resistance to the lithium component. The bending strength within this range can be adjusted by adopting an appropriate method as a molding method of the molded body to be baked in the manufacturing process of the kiln tool of the present invention. Examples of such a molding method are as described above.

The kiln tool of the present invention preferably has a low coefficient of thermal expansion coefficient of 25 × 10 ⁻⁶ / K or less, particularly 3.5 × 10 ⁻⁶ / K or less at 25 ° C. to 1200 ° C. Further, the elastic modulus is preferably 5 GPa or more, particularly 10 GPa or more at 25 ° C. When the kiln tool has a thermal expansion coefficient and an elastic modulus in this range, it is possible to further increase the number of times the kiln tool is repeatedly used in combination with excellent thermal shock resistance and high corrosion resistance to the lithium component. The thermal expansion coefficient and elastic modulus in this range can be controlled by adjusting the blending ratio of petalite and kaolin, which are raw materials used when manufacturing a kiln tool.

The kiln tool of the present invention preferably forms a powder containing petalite, more preferably a mixed powder containing petalite and kaolin into a target kiln tool such as a mortar, and the molded body is fired in an oxygen-containing atmosphere. It is manufactured by doing. Petalite, which is one of the raw materials, is a silicate mineral containing lithium and aluminum, and is a substance represented by Li (AlSi ₄ O ₁₀ ). Kaolin, which is another raw material, is a hydrous silicate mineral of aluminum, and is a substance represented by Al ₂ Si ₂ O ₅ (OH) ₄ . In this production method, petalite and kaolin are mixed in a powder having a predetermined particle size. The particle diameter D ₅₀ of petalite and kaolin in the mixed powder is preferably 1 to 1000 μm, and more preferably 1 to 100 μm, from the viewpoint of less variation of components in the manufactured kiln tool.

The blending ratio of petalite and kaolin affects the composition and properties of the ceramic material in the resulting kiln tool. From the viewpoint of increasing the ratio of β-spodumene in the ceramic material, and from the viewpoint of bringing the content ratio of Li ₂ O, Al ₂ O ₃ and SiO ₂ into a desired range, the mixing ratio of petalite and kaolin is petalite: kaolin = It is preferable to set it as 100: 0-20: 80, and it is still more preferable to set it as 70: 30-40: 60.

  The mixed powder of the raw material may contain only petalite and kaolin, or may contain other minerals in addition to petalite and kaolin. Further, as described above, there are cases where only petalite is used as the raw material powder, and kaolin may not be used.

Various molding methods such as hydraulic molding and cast molding can be used to obtain a molded body that is a precursor of a kiln tool using mixed powder of raw materials. In the case of using hydraulic forming, about 0.5 to 5% by mass of water is added to the mixed powder to form a water-containing fluid, and the water-containing fluid is filled in the mold cavity to perform pressure molding. Do. For the pressure molding, for example, biaxial pressing can be employed. The applied pressure is preferably set to about 200 to 800 kg / cm ² . By adjusting the applied pressure, the bulk specific gravity, porosity, and bending strength of the obtained kiln tool can be adjusted. The molded body thus obtained is dried to remove moisture and subjected to firing.

  On the other hand, when performing casting, about 20-50 mass% water and about 0.2-3 mass% dispersing agent are added with respect to mixed powder, and it is set as a slurry. As the dispersant, for example, a polycarboxylic acid-based dispersant can be used. The slurry is poured into a plaster mold and solidified. After demolding from the plaster mold, the molded body from which moisture has been removed by drying is subjected to firing.

  A desired kiln tool can be obtained by firing the compacts obtained by various molding methods in an oxygen-containing atmosphere such as air. Regarding the firing conditions, the firing temperature is preferably about 1000 to 1400 ° C. The maximum temperature holding time is about 2 to 10 hours when the firing temperature is within this range.

  Since the kiln tool of the present invention thus obtained contains β-spodumene, which is a ceramic material containing lithium, it is difficult for deterioration due to the lithium component contained in the raw material of the positive electrode active material to occur, and the number of repeated use Will be much improved. Moreover, it becomes the thing excellent in the peelability of the positive electrode active material which is a product. Furthermore, the spalling resistance is also high.

  In order to produce a positive electrode active material using the kiln tool of the present invention, for example, various powders that are raw materials for the positive electrode active material are mixed, and a predetermined amount of mixed powder is filled in the kiln tool. Then, the kiln tool filled with the mixed powder is installed in the firing furnace. As a baking furnace, well-known furnaces, such as a roller hearth kiln, a shuttle kiln, a tunnel kiln, and a pusher furnace, can be used. The firing atmosphere can be an oxygen-containing atmosphere including air. Although the firing temperature depends on the kind of the mixed powder, it can generally be about 950 to 1100 ° C. The firing time can generally be about 3 to 10 hours.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
40% petalite powder and 60% kaolin powder were mixed, and 2% of water was added to the mixed powder to obtain a hydrous fluid. The results of quantitative analysis of petalite and kaolin are shown in Table 1. The average particle diameter D ₅₀ of the powder mixture was 50 [mu] m. This hydrous fluid was filled in a mold and molded by biaxial pressing. The applied pressure was 800 kg / cm ² . The obtained molded body was naturally dried for 1 day and then dried at 100 ° C. for 1 day. The dried molded body was fired by being held at 1200 ° C. for 5 hours in an air atmosphere furnace to obtain a mortar as a target kiln tool. The mortar was a square with a bottom portion of 300 mm square, and the height of the wall portion was 200 mm. The wall thickness was 12 mm. Powder X-ray diffraction measurement was performed on the obtained mortar. The result is shown in FIG. As is clear from the results shown in the figure, it was confirmed that the mortar obtained in this example contains β-spodumene.

[Examples 2 and 3]
A molded body was obtained in the same manner as in Example 1 except that the composition of the raw material mixed powder was as shown in Table 2 below. The obtained molded body was fired in the same manner as in Example 1 to obtain a mortar. The obtained powdered mortar was subjected to the same powder X-ray diffraction measurement as in Example 1, and it was confirmed that the mortar contained β-spodumene.

[Examples 4 and 5]
The same petalite and kaolin used in Example 1 were mixed in the composition shown in Table 2 below. A slurry was obtained by adding 35% water and 1% polycarboxylic acid ammonium salt (dispersant) to the mixed powder. This slurry was poured into a gypsum mold, allowed to stand for 1 hour to solidify, and then demolded. The obtained molded body was naturally dried for 2 days and then dried at 100 ° C. for 1 day. The dried molded body was fired by holding at 1200 ° C. for 5 hours in an air atmosphere furnace to obtain a sagger having the same shape and dimensions as in Example 1. The obtained powdered mortar was subjected to the same powder X-ray diffraction measurement as in Example 1, and it was confirmed that the mortar contained β-spodumene.

[Comparative Example 1]
Spinel 60%, cordierite 20% and mullite 20% were mixed, and 2% of water was added to the mixed powder to obtain a hydrous fluid. This hydrous fluid was filled in a mold and molded by biaxial pressing. The applied pressure was 800 kg / cm ² . The obtained molded body was naturally dried for 1 day and then dried at 100 ° C. for 1 day. The molded body after drying was fired by holding it at 1350 ° C. for 5 hours in an air atmosphere furnace to obtain a target mortar.

[Evaluation]
About the mortar obtained by the Example and the comparative example, the composition analysis of each component was performed by the method mentioned above. Further, the apparent specific gravity, bulk specific gravity, porosity, thermal expansion coefficient (25 ° C. to 1200 ° C.), bending strength (25 ° C. and 1000 ° C.) and elastic modulus were measured by the methods described above. Furthermore, corrosion resistance was evaluated by the following method. The results are shown in Table 2 below. About Example 1, the longitudinal cross-section of the bottom face part of the mortar after producing lithium manganate was cut out after the corrosion resistance evaluation described below, and the structure of the cross-section was observed with an optical microscope. The result is shown in FIG. Furthermore, about Example 2, while cutting out the longitudinal cross section of the bottom face part of the mortar after manufacturing lithium manganate, and observing this cross section with a scanning electron microscope, element mapping of aluminum, silicon, and manganese was performed. . The result is shown in FIG.

[Evaluation method for corrosion resistance]
Lithium carbonate and manganese oxide (MnO ₂ , Mn ₂ O ₃ ) were mixed at a molar ratio of Mn: Li = 2: 1 to obtain a raw material powder of lithium manganate. 10 kg of this raw material powder was filled in the mortars obtained in the examples and comparative examples. This mortar was fired in a roller hearth kiln at 1000 ° C. for 5 hours to produce lithium manganate. This process was repeated, and the number of uses until a defect such as a crack occurred in the mortar was measured.

  As is clear from the results shown in Table 2, it can be seen that the mortar obtained in each example has higher corrosion resistance than the mortar of the comparative example. Moreover, as is clear from the results shown in FIG. 2 and FIG. 3, the mortar obtained in Examples 1 and 2 is not observed at the interface with lithium manganate and is derived from the raw material powder of lithium manganate. It can be seen that the corrosion resistance to the lithium component is high. Although not shown in the table, the content ratio of β-spodumene semi-quantitatively determined from the X-ray diffraction measurement results of the mortar obtained in each example was 10% by mass or more. Further, although not shown in the table, in each of the examples, the peelability of the manufactured lithium manganate from the mortar was good.

Claims (10)

  A kiln tool for producing positive electrode active materials for lithium secondary batteries made of ceramic materials containing β-spodumene. Content of li ₂ O is 1 to 12 wt%, the content of Al ₂ O ₃ is 15 to 45 mass%, according to claim 1, wherein the content ratio of SiO ₂ is 55 to 75 wt% Kiln tools. The kiln tool according to claim 1 or 2, wherein the content ratio of Na ₂ O is 1% by mass or less, the content ratio of K ₂ O is 2% by mass or less, and the sum of both is 3% by mass or less.   The kiln tool according to any one of claims 1 to 3, having a bulk specific gravity of 1.5 to 2.5.   The kiln tool according to any one of claims 1 to 4, wherein the porosity is 5 to 40%.   The kiln tool according to any one of claims 1 to 5, wherein a normal temperature bending strength measured in accordance with JIS R2619 is 5 to 60 MPa. The kiln tool according to any one of claims 1 to 6, wherein a thermal expansion coefficient at 25 ° C to 1200 ° C is 5 × 10 ^-6 / K or less.   The kiln tool according to any one of claims 1 to 7, wherein an elastic modulus is 5 GPa or more. The kiln tool according to any one of claims 1 to 8, wherein a content ratio of Fe ₂ O ₃ is 0.5 mass% or less. It is a manufacturing method of the kiln tool according to claim 1,
A method for producing a kiln tool comprising the steps of forming a mixed powder containing petalite and kaolin into a desired kiln tool shape and firing the molded body in an oxygen-containing atmosphere.